For a \(1\rightarrow 2\)  decay amplitude, the conventional Lorentz tensor decomposition and projection method
can be carried out quite simply (due to the limited number of basis structures and scales).
For instance, for the fermion's gauge interaction vertex a general form factor decomposition
can be found in [1]}.
Here we briefly comment on how one can compute polarized \(1\rightarrow 2\)  decay amplitudes if one wants
to use the above prescription.
